Removes PIXI global object in ES and CJS bundles to enable tree-shaking (#5399)

Removes PIXI.loaders namespace, adds consistent loader plugin structure (v5) (#4471) ...

* Remove inline loader middleware install

* Removes PIXI.loaders namespace, adds PIXI.Loader.registerPlugin

Decouple Canvas Functionality (v5) (#4429) ...

* Create canvas-renderer package

* Externalized all canvas-related functionality as packages

* Creates pixi-modern package (no canvas)
* Renames PIXI.WebGLRenderer to PIXI.Renderer
* Removes “WebGL” from class names, makes default

* Include modern build to Travis deploy

* Fixes linting issue

* Fixes app test on Travis

* Fixes Travis issues with app-loader mixin

* Add missing CanvasRenderer from accessibility tests

* More de-coupling, using _renderCanvas mixins, pixi.js inherits pixi-modern

* Re-adds missing dependency

* Re-adds other missing dependencies

* More strict comments elimination

* pixi-modern as a dependency is slow and bloated, undoing

* Fix ES global object

* Moves pixi.js to pixi.js-legacy

* Move pixi-modern to pixi.js

* Shared deprecations between bundles

* Adds unit tests for window

* Reorganized canvas and filter packages

* Renames renderWebGL functions to render

* Creates new canvas-display package for last of canvas functionality

# Conflicts:
#	bundles/pixi.js/src/index.js

* Removes preprocess, better deployment

* Removes deprecation packages, pixi.js-legacy now inherits pixi.js